Unvented Undersink Water Heaters. For D.I.Yers.

A plumber once told me that they are not permitted to be used where they are inaccessible. In other words, the situation is just like MF JBs.

I think the old rules were something like that - you couldn't use olive-type compression fittings underground, but you could use ‘manipulative’ fittings - i.e. ones that didn't have a loose olive but instead used a special tool to create an olive shaped bulge in the copper tube itself.

Probably the rules have changed these days to allow plastic compression fittings with MDPE underground pipework (where the seal is by O-ring but the restraint is often compression of some form). 

   - Andy.

A plumber once told me that they are not permitted to be used where they are inaccessible. In other words, the situation is just like MF JBs.

I think the old rules were something like that - you couldn't use olive-type compression fittings underground, but you could use ‘manipulative’ fittings - i.e. ones that didn't have a loose olive but instead used a special tool to create an olive shaped bulge in the copper tube itself.

Probably the rules have changed these days to allow plastic compression fittings with MDPE underground pipework (where the seal is by O-ring but the restraint is often compression of some form). 

   - Andy.